Now wastewater use is gaining steam in the developed world too, though in rich countries, the water undergoes a cleansing process before being pumped out to taps.

"Wastewater recycling is something we will have to rely more heavily on," said Shivaji Deshmukh, program manager for the groundwater replenishment system at the Orange County Water District in southern California.

Orange County has been recognized for its innovative sewage system, which collects what people flush down the toilet, separates its components, then treats the wastewater to drinking-water standard.

The county water district pumps the treated wastewater into underground caverns, where it is stored and later used as tap water or irrigation water.

In the U.S. many federal and state laws require reclaimed water to sit in rivers or aquifers before it can be processed for drinking water.

This explains why water coming out of the Orange County facility doesn't flow directly to residents' taps, Deshmukh said.

The Groundwater Replenishment System facility, the largest of its kind, supplies 70 million gallons (265 million liters) of treated water a day, enough for 500,000 people.

Fighting Drought

Like many other regions, Orange County is struggling to find fresh water during prolonged periods of drought.